Process of recovering hydrocyanic aged



"G.H'.BUCHANAN.,

PROCESS 0F RECOVERING HYDROCYANIC ACID. APPLICATION FILED MAY?, 1919.

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GUY H. BUCHANAN, 0F BOSELLE, NEW J ERSEY, ASSIGNOR TO AMERICAN CYANMIDCOMPANY, 0F NEW YGRK, N. Y., A. CORPORATION 0F MAlNE.

PROCESS 0F BECOVERING HYDROCYNIC ACID. y

Specification of Letters Patent.

Patented oet. 7,' rare.

Application filed Hay 7, 1919. Serial No. 295,299.

To all whom t may concern.'

Be it known-that L GUY H. BUCHANAN, a y citizen of the United States,residing atRoselle, in the county of Union and State of N ew Jersey,have invented certain new and useful Improvements in Processes ofBecovering Hydrocyanic Acid; and l do hereby declare the following to bea full, clear, and eXactdescription of the invention, suc-h as willenable others skilled in the art to which it appertains to make and usethe same.

This invention relates to a process of .recovering high gradehydrocyanic acid from a. crude form of cyanid, and has for its object toprovide a method of obtaining such high grade product from low grade rawmaterials which will be more eitcient and less costlyv than -thoseheretofore proposed.

With these and other objects in view the invention vconsists in thenovel steps and combinations of steps constituting the process. all aswill be more fully hereinafter disclosed, and particularly pointed outin the claims.

ln order that the precise nature o this invention may be the moreclearly understood it is said It is well known in the art that when theordinary sodium orl potassium Cyanid of commerce, containing say Qtr-98%of the corresponding cyanid, is treated with a strong vmineral acid,hydroc-yanic acid is evolved and a conesponding sodium or potassium saltof the mineral acid used is left behind in the residue. F or instance,in the case of sodiumcyanid and sulfuric acid, the reaction takes placeaccording-to the well known equation- The usual method heretoforeemployed of carrying out this operation was to place in a closed vesselya quantity of sulfuric acid, of a strength varying from comparativelydilute acid up to 66 Baume. although the? majority of operators preferthe more dilute acid. It was then the practice to drop powdered or lumpcyanid into the acid, the lump form being preferred, as yieldingsomewhat more hydrocyanic acid than the powdered form, especially whenthe cyanid is not substantially pure.

Later developments, however, in this art have shown it practical todissolve the pure forms of cyanifl in lWater and ,to then add thesolution to the sulfuric acid in a suitable generating vessel.

rlhis practice which has been quite highly developed since the outbreakof the European war, has shown eiiiciencies of hydrocyanic acidproduction upward of 75% but rarely have eiiciencies as high as 85% beenobtained in long practice, and published reports of recent work inconnection with poison gas have shown less than 80% for standardpractice.

a crudeV or impure form of cyanid made from cyanamid and which may beconsidered to contain approximately 35% sodium cyanid, 40% calciumchlorid, 5% sodium chlorid, 15% of lime and 5% of miscellaneousimpurities coming from the cyanamid and playingy no essential part inthe operation. `When this said crude cyanid material is treated in thesame manner as the pure cyanid, extremely poor results are obtained, theyield of hydrocyanic acid gas being usually less than 7 0% and in man vinstances as low as 50%. The said crude cyanid can not .bedissolvedcompletely in water because it contains-a considerable percentage oinsoluble lime and other impurities, and further, if one attempts toprepare a solution the hydration of the lime causes the evolution ofconsiderable heat, and 1t 1s well lmown that hot solutions of cyanidrapidly and spontaneously decompose.

Upon the treatment of this crude cyanid l with a mineral acid, such assulfuric acid,

apptus as is used in the pure cyanid.

In the present lnventionl propose to use `The common practice heretoforerecommended for the production of prussic acid involves the running of asolution of cyanid into the sulfuric acid. In such case, an excess ofsulfuric acid ismaintained in the` generator throughout the majorportion ofy the reaction and-this excess acid, for instance, could reactupon the chlorids present in the crude cyanid forming hydrochloric acid,which would be evolved along wit-h the prussic acid, and not onlycontaminate the latter, but also give rise to serious corrosiondifficulties in the apparatus used for recovering the prussic acid. Itis therefore, necessary in handling the crude cyanid to prevent any suchevolution of hydrochloric acid, and the present invention presents a wayof successfully using crude cyanid such as described above, for theproduction of pure prussic acid.

In carrying out the presentprocess, I proceed in the following manner,reference being had to the accompanying drawing forming a part of thisspeciiication in which the figure is a diagrammatic sectional view of`one form of apparatus suitable'therefom- Into a suitable generatingvessel 1 made of acid resisting material, I introduce a predeterminedquantity of water, for example, three or four times the weight of thecrude cyanid I vintend to use, and to this said water I add the saidcrude cyanid in the form of dry thin flakes such as it occurs on theopen market. Or I may charge the dry flakes into vthe generator and thenadd to it the requisite quantity of water as indicated above, it notaffecting the process as to which method of operation is used. Iimmediately close up the generator ,l and as rapidly as possible run' inthe equivalent amount of sulfuric or other mineral acid necessary fordecomposing the sodium cyanid in the crude cyanid added. yThe limepresent being a strongly alkaline compound,

with a greater aiinity for acid than the sodium cyanid, naturally myacid addition must also be ample to take care of the free lime present,but in'no case do I add suffe cient acid to more than take care of thealkalinity ofthe solution, and the sodium cyanid present, althougho aysmall excess of sulfuric acid is not harmful if this said excess is notltoo great. It is not necessary to add sulicient acid to decompose thechlorids completely or ity,`my acid addition amounts to approxisodiumcyanid.v

The acid is run in quite rapidly through in fact in any considerablepart. For example, the common practice in carrying out the prior processabove mentioned is to add one part 66 B. sulfuric acid to one part 9698%sodium cyanid; whereas in the case of crude cyanid, on account of itsalkalinmately l times as much as is used in the case of pure cyamd forthe samelcontent of a supply pipe/2,z consuming less' than ten minutesfor a charge of as much as 500 pounds of crude 'cyanid at an operation.The solution in the generator heats up and a considerable quantity ofprussic acid is evolved and passes out through a pipe 3 to the recoveryapparatus, not shown. The rest' of the prussic acid generated dissolvesin the bulk of `the solution used and I indit a simple mat-ter to drivethis out by the direct introduction of a very small quantity of steamwhich is forced from a pipe 4 through' the solution in the generator.IBy operating in this way, I have repeatedly obtained 93% recovery ofhydrocyanic acid in fairly concentrated form and havel at times obtainedas much as These recoveries are considerably above those obtained in theolder process operating on pure cyanid. Y

To avoid the contamination AofI the hydrocyanic acid by hydrochloricacid I make the acid addition at the bottom of the generator andunderneath the surface of the emulsion of crude cyanid and Waterpresent. In this way I always have present an excess of unreactedcyani'd which would be decomposed by any hydrochloric'acid set free inthe bottom of the apparatus and consequently I obtain hydrocyanic acidpractically free' from 'hydrochloric acid. In many experiments I `havefound no hydrochloric acid or at most traces in undeterminate quantitiesin my recovered hydrocyanic acid. To insure absolute freedom from eventraces of hydrochloric acid, I may insert in the pipe line 3 conveyingthe hydrocyanic Y acid to the recovery plant lumps of lime stone 5 whichabsorb the hydrdchloric acid and do not react upon hydrocyanic acid.This apparatus is simple and easy to main-l tain and the oonsumptionoflime stone for long time operation .is practicably negligible. I amaware that it has been proposed to steam jacket generators for makinghydrocya-nic acid but I have found it a very decided'improvement todirectly introduce livesteam in the generator and I thereby ascribe myextremely high recoveries ih' part to this introduction of l1ve steamdirectly into thek generator.

The hydrocyanic acid produced byl the present method of generation is ofessen- ,may vary the details of the above procedure wlthout departingfrom the spirit of the invention` and therefore, I do 110i" wish t0 b@limited to the above disclosure except as `may be required by theclaims.

What I claim is l 1. The process of producing hydrocyanic acid from rawmaterial containing a substantial percentage of impurities, whichconsists in mixing said raw material with water; subjecting' saidmixture to the action 'of a mineral zicid introduced beneath the surfaceof said mixture, whereby hydrocyanic acid gas is evolved; subjectingsaid mixture to the direct action of steam, whereby any gas which may bedissolved in said mixture is driven oi'; passing the evolved gas througha scrubber; and suitably recovering said hydrocyauic acid gas,substantially as described.

2. rlhe process of producing hydmcyanic acid from ycrude cyanids derivedfrom cyanamid and which contain a substantial percentage ofinsolubleimpurities, which consists in mixing said crude cyanids with water toform an emulsion; introducing sulfuric acid beneath the surface of saidemuling o hydrocyanic acid gas; passing steam gas through a `scrubber;and suitably recovering said hydrocyanic acid gas, substantially asdescribed.

3. rlhe process of producing hydrocyainc` acid from crude cyanids whichcontain a substantial percentage of impurities in the form of chloridswhich consists in mixing said crude cyanids with water; subjecting saidmixture to the action of sulfuric acid introduced beneath the surfacethereof, whereby 'hydrocyanic acid. gas is evolved and any hydrochloricacid produced is caused to react with lthe cyanids present; passingsteam through said mixture to drive ofi'l any of the evolved gas whichmay be dissolved therein; and collecting and treating said evolved gasto remove any hydrochloric acid passing over therewith, substanv tiallyas described.

4. The process of increasing the yield of substantially pure hydrocyanicacid obtainable from low grade cyanids derived from cyanamid and whichcontain alkaline imthrough the said mixture to drive off any ofthe saidgas which may be Vdissolved therein; suitably treating the said gas toremove any impurities` therefrom; and suitably recovering the saidtreated gas,- substantially as described.

5. The process of producing substantially pure hydrocyanic acid from lowgrade cyanids which contain a substantial percentage of impurities inthe form of chlorids and lime which consists in mixing said low gradecyanids with water; treating said mixture with a suiicient quantity ofsulfuric acid to neutralize the limey present and to decompose thecyanids to evolve hydrocyanic acid gas; introducing steam be- -low thesurface of said mixture to drive olf acid from low grade cyanids whichcontain a substantial percentage ofimpurities in the form of chloridsand lime which consists in mixing said low grade cyanids with water toform an emulsion; treatingsaid emulsion with a sufficient quantity ofsulfuric acid to neutralizel the same and to reactwith the cyanidsYpresent to evolve hydrocyanic acid gas, the said sulfuric acid beingintroduced below the surface of said emulsion whereby any hydrochloricacid produced is caused to react with said cyanids; introducing steambelow the surface of said emulsion to drive od any of the hydrocyanicacid gas-which may be dissolved therein; passing said gas through a limestone scrubber to remove any hydrochloric acid contained therein; andsuitably recovering said gas, substantially as described.

7. The process of producing hydrocyanic acid from low grade cyanidswhich contain a substantial percentage of impurities in the form ofchlorids and lime` which consists in mixing said low ter to form anemulslon; treating said emulsiony with a suicient quantity of 'sulfuricacid .to neutralize the same and to react with the cyanids present toevolve hydrocyanic acid gas, the vsaid sulfuric acid being introducedbelow the surface of `said emulsion whereby any hydrochloric acidproduced is caused to react with said cyanids; lntroducing steam belowthe surface of said purities which consists in mixing said low' gradecyanids with water; adding to said mixture a suiicient quantity of amineral acid to substantially neutralize the same and to decompose thecyanid present, drivemulsion to drive 0H any ofthe hydrocyanic acid gaswhich may be dissolved there.- in; passing said gas through a rectifyingcolumn; and suitably recovering said gas, substantially as described.

ade cyanids with waf 8. The process of produclng llydrocyanicl acid fromlow grade cyanidsv which contain a substantial percentage of impuritiesin the form of chlorids and lime which consists in mixing said low gradecyanids with Water t0 form an emulsion; treat-ing said emulsion with asufficient quantity of sulfuric acid to neutralize the saine and toreact with the cyanids present to evolve hydrocyanic acid gas, the saidsulfuric acid beingintroduced below the surface of said emulsion wherebyany hg; drochloric acid produced is caused to react `with said cyanids;introducing steam below the surface of said emulsion to drive ol' any ofthe hydrocyanic acid gas which may be dissolvedv therein; passing saidgas through a combined limestone scrubber and rectifying column; andsuitably recovering 15 said gas, substantially as described.

In .testimony whereof I aiix my signature, in presence of two Witnesses.

GUY H. BUCHANAN. Witnesses:

E. M. FITZGERALD, E. H. BOHN.

